Precoated metal sheets and manufacture thereof

ABSTRACT

A precoated metal sheet for producing a metal working product which comprises a base metal sheet, a coating film of a thermosetting resin which is formed on the base metal sheet and cured to semi-hardened state having a tackiness of from 2.0 to 40 g/cm width at a temperature of 25* C and at a relative humidity of 75% and a polyolefin sheet adhered to the above semi-hardened coating film; and a method for manufacturing the precoated metal sheet.

United States Patent [191 Matsudaira et al. 7

[ 51 Mar. 18, 1975 1 1 PRECOATED METAL SHEETS AND MANUFACTURE THEREOF[75] Inventors: Tadashi Matsudaira; Minoru Namiki, both of Hiratsuka,Japan [73] Assignee: Kansai Paint Company Limited,

Amagasaki-shi, Hyogo-ken, Japan [22] Filed: Oct. 4, 1972 [21] Appl. No.:294,917

[30] Foreign Application Priority Data Oct. 1 l, 1971 Japan 46-80405[52] US. Cl. ..117/6,117/75,l17/132 B, 117/132 BE, 117/132 BF, 161/213,161/214, 161/216, 161/186, 161/215, 161/218,

[51] lnt. Cl B32b 15/04 158] Field of Search 161/2l3,2l4,216; 117/6,117/75 [56] References Cited UNITED STATES PATENTS 2.858.248 10/1958Hastings ct a1. 161/214 2,992,132 Melamed 117/75 3,202,523 8/19653,442,752 5/1969 Sandler 161/214 3,454,520 7/1969 West et a1 117/63,455,865 7/1969 Bolt et al. 117/6 3,505,143 4/1970 Haas et a1. 161/2163,544,391 12/1970 Scott et a1 l6l/216 3,568,486 3/1971 Rosenberg et a1.117/75 3,650,809 3/1972 Gilliam et a1. 117/75 Primary ExaminerGeorge F.Lesmes Assistant ExaminerWi11iam R: Dixon, Jr. Attorney, Agent, orFirmLarson, Taylor and Hinds [57] ABSTRACT 2 Claims, 2 Drawing Figures iAIENTED KARI 819. 5

PRECOATED METAL SHEETS AND MANUFACTURE THEREOF This invention relates toa precoated metal sheet and manufacture thereof, more particularly to aprecoated metal sheet for producing shaped articles by metal workingwith a coating film formed thereon.

It has long been practiced to shape an uncoated metal sheet in asuitable form and then apply a coating composition to the resultingshaped product. Because of the necessity to coat the shaped metalworking products individually, this method is unfit for mass production,fails to give products of a uniform quality and renders the resultingproducts costly. On the other hand, so-called precoating process hasbeen developed in which a coating composition is previously applied to ametal sheet material with or without conducting pretreatment orconversion coating, and the metal sheet mm/min. The peeling load readingon the balance provides a tackiness value. The measurement was conductedat a temperature of 25C at a relative humidity of 75%. The greater thevalue, the more difficult it is to peel the film off.

The base metal sheets to be used according to this invention are a widevariety of metal sheets which have heretofore been used, such as mildsteel sheet. aluminum sheet, chromium-plated steel sheet. zinc-platedsteel sheet, etc. Employable as the compositions for forming thesemi-hardened coating film are those containing as a binder athermosetting resin, such as for example, (l) thermosetting acrylicresin containing hydroxyl group in the molecule and having. an acidvalue material thus precoated is then shaped after hardening An objectof the invention is to provide a precoated metal sheet from which shapedmetal working products can easily be obtained free from cracking orpeeling of the coating film.

Another object of the invention is to provide a precoated metal sheetfor producing the shaped metal working products having hard coatingswhich are excellent in physical and chemical properties such ashardness, abrasion resistance, scratch resistance, strain resistance,chemical resistance, etc.

Another object of the invention is to provide a precoated metal sheetfor producing shaped metal working products, which is free from blockingphenomenon even when placed in layers or rolled up.

Another object of the invention is to provide a method for producing aprecoated metal sheet having the above excellent characteristics.

These and other objects and advantages of the invention will be apparentfrom the following description.

The precoated metal sheet of the invention comprises a base metal sheet,a coating film ofa thermosetting resin which is formed on the base metalsheet and cured to semi-hardened state having a tackiness of from 2.0 tog/cm width at a temperature of 25C and at a relative humidity of 75%,and a polyolefin sheet adhered to the above semi-hardened coating film.

Throughout the specification and claims tackiness is determined by thefollowing method:

A combination of a balance and constant speed peeling device is used asa tester. A precoated metal sheet having semi-hardened state coatingfilm is adhered to protective polyolefin sheet and pressed at a pressureof 0.2 kg/cm with a rubber roll having a hardness of 70 determinedaccording to MS K 6301 5.1 (l). The precoated metal sheet with aprotective polyolefin sheet adhered thereto is left to stand at roomtemperature for 24 hours and cut into a piece 25 mm wide by about 20 cmlong. The protective sheet is peeled off about 1 to 2 cm long from theupper end of the specimen, which of 5 tov 20 and hydroxyl value of'lO to70, parts by weight of this resin being used with 20 to 60 parts byweight of melamineformaldehyde resin and/or not more than 20 parts byweight of bisphenol A- epichlorohydrine type epoxy resin having an epoxyequivalent of 300 to 800; (2) alkyd-melamine resin comprising 100 partsby weight of alkyd resin modified with non-drying oil and/or non-dryingoil fatty acid and having an oil length of 10 to 30 and 20 to 60 partsby weight of melamineformaldehyde resin; (3) bisphenolA-epichlorohydrine type epoxy resin having an epoxy equivalent of 800 to4,000, 100 parts by weight of this resin being used with 20 to 60 partsby weight of butyletherified phenol-formaldehyde resin or with 20 to 60parts by weight of-butyl-etherified urea-formaldehyde resin; and (4) oilfree polyester-melamine resin comprising 100 parts by weight of oil freepolyester having an acid value of 5 to 20 and hydroxyl equivalent of 400to 1,300 and 20 to 60 parts by weight of melamineformaldehyde resinmodified with an aliphatic monoalcohol having from 1 to 4 carbon atoms.Such coating 1 composition usually comprises 100 parts by weight of thethermosetting resin binder, not more than parts by weight of extenderpigment, not more than 100 parts by weight of coloring pigment and, ifdesired, not more than 20 parts by weight of plasticizer. Solvents areadded to the composition in such an amount that the resultantcomposition have a viscosity of 30 to 200 see, preferably 100 to 120sec. (at 25C, Ford cup No. 4). The solvents to be used may be any of awide variety of those usually employable as solvent. Particularlypreferable are mixed solvents comprising aromatic hydrocarbons andcyclohexanone, ethyleneglycol mono;

butyl ether, butanol, B-ethoxy-ethyl acetate, or lik polar solvent addedthereto. The plasticizers to be are volatile plasticizers such asdimethylphthalate, diethylphthalate, triethyleneglycol monoethyl ether,diethyleneglycol monobutyl ether, etc. Solvents having a boiling pointof more than 200C also serve as plastiple by using roll coater orcurtain flow coater. The

coating composition to form a semi-hardened top coat film is applied toa thickness of about 5 to 50 microns whendried. The baking conditions,which may'vary depending on the kind of the coating compositions used,are usually a temperature of 70 to 190C and a baking time of about 30 to90 seconds so as to produce a semihardened coating film having athickness of 2.0 to 40 g/cm width, preferably 5 to g/cm width. Apolyolefin sheet is then applied over the coating film which hasbeensemi-hardened by baking. If the tackiness of the coating film islessthan 2.0 g/cm width, the polyolefin sheet is liable to peel off fromthe coating film. On the other hand, if it is more than 40 g/cm width,the polyolefin sheet will be torn when peeled off from the shaped metalproduct obtained by shaping the present metal sheet. The polyolefinsheets to be used for this purpose are, for example, those ofpolyethylene, polypropylene and the like. Preferably, the sheet isusually about 0.02 to 0.2 mm in thickness. The polyolefin sheet can beapplied to achieve the desired results by placing the sheet over thesemi-hardened coating film. Since the coating film is in the specificsemi-hardened state, the polyolefin sheet can be adhered to thesemihardened coating film without using any adhesive or tackifyingagent, to such extent that it will not be peeled off while transportedor shaped. After shaping of the precoated material, the polyolefin sheetcan be peeled off satisfactorily without damaging the coating film. Thuswe have found a novel fact that the semi-hardened coating film permits apolyolefin sheet to be adhered thereto without using any adhesive ortackifying agent and that the sheet can be peeled off ideally withoutdamaging the coating film.

The precoated metal sheet of this invention can be shaped by any desiredworking process. The polyolefin sheet is then peeled off thesemi-hardened coating film, and the coating film is thereafter baked forcomplete hardening. The coating film on the precoated metal sheet ofthis invention, being in semi-hardened state, is free from cracking orpeeling even when the metal sheet is shaped. In addition, the polyolefinfilm on the semi-hardened coating film protects the coating film fromdamage during shaping. The product of this invention has anotheradvantage of being free, for example, from damage when it is transportedafter shaping and before the semi-hardened coating film is completelybaked for finishing, since the plastic film protects the semi-hardenedcoating film. The metal working product thus obtained has a coatingwhich is excellent in hardness, abrasion resistance, stain resistance,and chemical resistance and is free from any cracking or peeling as wellas from all the drawbacks of the conventional precoating process,assuring full utilization of its advantages.

In the present invention various modifications can be conducted withoutdeparting from the spirit and scope thereof. For example, primer can beapplied to the metal sheet prior to the application of the compositionfor forming semi-hardened coating film in order to improve adhesionproperty and corrosion resistance. The primer may be a wide variety ofthose conventionally used. For example, coating compositions of theepoxy resin or vinyl resin type are chiefly used. The composition of theepoxyresin type, for instance, comprises 60 to 100 parts by weight ofepoxy resin, not more than 40 parts by weight of melamine, urea orphenolic resin,

not more than 50 parts by weight of extender pigment, not more than 50parts by weight of rust-proofing pigment and a suitable amount ofsolvent. The coating composition of the vinyl type comprises 60 to partsby weight of vinyl chloride-vinyl acetate copolymer resin, not more than40 parts by weight of epoxy resin, notmore than 40 parts by weight ofphenolic resin, not more than ,50 parts by weight of extender pigment,not more than 50 parts by weight of rust-proofing pigment, and asuitable amount of solvent. The primer is applied to such a thickness asto form an approximately 0.5 to 10 micron thick coating when dried andthe coating is baked at a temperature of to 250C for 20 to 60 seconds,whereby it is completely baked and hardened. If baking for hardening isinsufficient, the coating will have poor adhesion to the metal sheet;hence the need for complete baking and hardening.

For a better understanding of the invention examples are given below, inwhich the parts and percentages are all by weight. The photographsreferred to in examples are as follows:

FIG. 1 is a photograph showing the surface of can obtained in Example 1;and

tained in Comparison Example 1.

EXAMPLE 1 An aluminum sheet of 0.5 mm in thickness was degreased and itssurface was subjected to conversion coating with Bonderite 722 (Trademark, product of Nippon Parkerizing Co., Ltd., Japan). Bonderite 722" ismixture comprising phosphoric acid, chromic acid and sodium fluoride asprincipal ingredients. The sheet was then coated by a roll coater withan epoxy type coating composition given in Table 1 below as a primer andthen with a thermosetting acrylic coating composition given in Table 1below for a top coat, respectively followed by baking. The primer wasfully hardened by baking, whereas the top coat was baked to semihardenedstate of a tackiness of 20 g/cm width. A 17 micron thick polyethylenefilm was then applied over the resulting coating, and the product wasshaped into a square can by stamping. The polyethylene sheet wasthereafter peeled off, with the result that the coating surface wasfound to be free from any cracking and peeling. Thev shaped articleobtained was baked at a temperature of 200C for 10 minutes to effectcomplete hardening. The surface of the resulting product, as thephotograph of FIG. 1 shows, is free from any cracking or peeling.Further the coating obtained had the properties listed in Table 2.

COMPARISON EXAMPLE 1 The same aluminum sheet was coated with exactly thesame primer and top coat forming composition and baked in the samemanner as in Example 1, except that the top coat was also completelybaked and hardened. The resulting product was then shaped into a squarecan by stamping, with the result that, as shown in the photograph ofFIG. 2, marked cracking and apparent peeling were observed. Theproperties ofits coating are set forth in Table 2 below.

COMPARISON EXAMPLE 2 A shaped article was prepared by conducting thesame treatment as in Example 1 and using the same primer as in Example1, except that a coating composi- .5 tion presently used for precoatedmetal was applied to form a top coat, the coating composition comprising160 parts of a 50% Xylol solution of acrylic copolymer(copolymer ofstyrene, n-butyl acrylate, hydroxyethyl methacrylate and acrylic acid ina weight ratio of 70 l5 2), 40 parts of U-van 20 SA (Trade mark,butylated melamine resin, product of Mitsui Toatsu Co., Ltd., Japan), 80parts of titanium oxide, parts of Solvesso 100 (Trade mark, mixedsolvent of the aromatic hydrocarbons, product of ESSO Standard Oil Co.,U.S.A.), and 30 parts of B-ethoxy-ethyl acetate. The coating obtainedhad the properties shown in Table 2 below.

EXAMPLE 2 A zinc-plated iron sheet, 0.3 mm in thickness, was degreased,with its surface thereafter subjected to'conversion coating withBonderite 3300 (Trade mark, product of Nippon Parkerizing Co., -Ltd.,Japan): Bonderite 3300 is principally zinc phosphate. The sheet wascoated by a curtain flow coater with a vinyl type coating compositiongiven in Table 1 below as a primer and with a thermosetting aminoalkydtype coat- EXAMPLE 3 l0 Can-Super (Trade mark, 0.24 mm in thickness,

chromium-plated steel sheet, product of Shin Nihon Seitetsu Co. Ltd.,Japan) was coated with an acrylic coating composition by a roll coaterand set to semihardened state having a tackiness of 28 g/cm width in 15the same manner as in Example 1. The sheet thus treated was then shapedin to a cylindrical cup by a press. The film adhered was a polyethylenesheet, 17 microns in thickness. The composition of the coating materialis'shown in Table 1 below, and coating condi- 20 tions and properties ofthe coating as determined by testing are given in Table 2 below.

The coating had very excellent properties as in Example 1.

Table 1 Example 1 Example 2 Example 3 1. Primer Epikote 1007 80 VinyliteVMCH" 90 (Epoxy resin, product parts (Vinyl resin, parts of ShellChemical product of Union Co., U.S.A.) Carbide Corp.. U.S.A.) ResinBeckamine P-354" 40 Epikote 828" l0 (Butylated urea resin, parts (Epoxyresin, parts product of Dainihon product of Shell Ink Chemical Co.,Ltd., Chemical Co., U.S.A.) Japan) Pigment Zinc chromate 20 Titaniumdioxide 40 parts parts Solvesso 100" Xylol 140 (Trade mark, definedparts parts Solvent in Comparison Example 2) B-ethoxyethyl acetate 65Isophorone 140 parts (Ketone solvent, parts product of Union CarbideCorp, USA) Total 270 Total 420 parts parts 2v Top coat forming C omp.

50% acrylic l40 Cardura 30 Duracron RE. 487" 160 copolymer parts (Trademark, parts (Trade mark, parts solution alkyd resin, acrylic resin,(Copolymer of product of product of Mitsubishi styrene, Shell ChemicalRayon Co., Ltd., ethylacr late, Co., U.S.A.) Japan) hydroxy ethylmetacrylate and acrylic acid in a weight ratio of40145 l5:l2, dissolvedin a 8 2 weight ratio mixture of xylol and butanol) Resin U-van 20 SA 60U-van 20 SA Epikote l 10 (Trade mark, parts (Trade mark, parts (Trademark, parts defined in defined in epoxy resin, Comparison Comparisonproduct of Example 2) Example 2) American Cyanamid Co., U.S.A.)

Cymel 300" 10 (Trade mark, parts melamine resin, product of AmericanCyanamid Co., U.S.A.)

Table 1 Continued Example I Example 2 Example 3 Pigment Titanium 80Titanium 80 Titanium I 80 dioxide parts dioxide parts dioxide partsPlasti- Dimethyll5 Triethylene Diethylene 30 cize'r phthalate partsglycol parts glycol parts monoethyl A monobutyl ether ether Solvesso 2SSolvesso Solvesso 30 I00" parts I00" parts I00 parts (Trade mark, (Trademark, (Trade mark, defined in defined in defined in ComparisonComparison Comparison Example 2) Example 2) Example 2) Solvent B-ethoxy-2S Butanol l0 B-ethoxy- 25 ethyl parts parts ethyl parts acetateacetate.

- Total 345 Total 330 Total 345 parts parts parts Table 2 Comp. Comp.Example 1 Ex. 1 Ex. 2 Example 2 Example 3 Coating and baking conditionsBaking temp. 200C 200C 200C 150C Primer Baking time 40 sec. 40 sec. 40sec. 30 sec. coat Dry coating 3 p. 3 p. 3 tr 7 p. thickness Baking temp.100C 200C 250C C 180C Top coat for semi- Baking time 60 sec l0 min. 60sec. sec. 40 sec. hardening Dry coating thickness 25 a 25 p. 25 a 40 p.10 p.

Tackiness 2O g/cm 0 0 l6 g/cm 28 g/cm width width width Top coat Bakingtemp. 200C C 250C for complete Baking time 10 mm. 20 mm. 2 mm. hardeningState of No cracking Coating Slight No cracking No cracking shapedportion and peeling film cracking and peeling and peeling (inspected incoating cracked n coatin coating in coating with unaided film and mgfilm film film eye) peeled markedy Pencil 3H 3H H 3H 3H hardnessAbrasion Properties resistance 8.0 mg 8.5 mg 12.5 mg 5.0 mg 8.0 mg ofcoating lStain resistance Spirit ink (red) Good Good Stained Good Goodmarkedly Spirit ink (black) Good Good Stained Good Good markedlyLipstick (No. 614, product of lsehan Co., Good Good Stained Good GoodJapan) markedly Lipstick (No. 615. roduct of of lsehan 0.. Good GoodStained Good Good Japan) markedly Chemical resistance No No SoftenedGood No change change chimtlc The properties of coating were determinedby the following test methods:

*1 Tackiness The same as disclosed before.

*2 Pencil hardness v Determined according to H8 K 54006.14 (70).

*3 Abrasion resistance 'lcst was conducted on a Tabers Abraser, using aweight of 500 g and a CS-lO abrading wheel. The result was expressed interms of the amount of coating "'orn away after 300 revolutions.

*4 Stain resistance The coating was stained with spirit ink (red andblack) and lipstick and then left to stand at room temperature for 24hours. The surface of coating was wiped with absorbent cottonimpregnated with ethanol. If the surface was found free from stain orcolor, the result was interpreted as good.

*5 Chemical resistance A glass ring (about mm in inner diameter and mmin height) was placed on the coating in snug-fit contact therewith andcompletely sealed with vaseline or paraffin. A 5% aqueous solution ofacetic acid was poured into the ring to approximately one hall itsheight and the ring was covered with a glass plate. The specimen wasretained in horizontal position and left to stand at room temperaturefor 6 hours. The ring was then removed from the specimen, which wasthereafter dried in the indoor air for 1 hour. Subsequently, the stateof the coating was inspected.

What we claim is:

1. A precoated metal sheet for producing a metal working product whichcomprises a base metal sheet, a coating film of a thermosetting resit.hich is formed on the base metal sheet and cured to semi-hardened statehaving a tackiness of from 2.0 to g/cm width at a temperature of 25C andat a relative humidity of 75% and a polyolefin sheet removably adheredto the above semi-hardened coating film; said base metal sheet being onespecies selected from the group consisting of mild sheet, aluminumsheet, chromium-plated 5 steel sheet and zinc-plated steel sheet; saidthermosetting resin being one species selected from the group consistingof l. thermosetting acrylic resin containing hydroxyl 2. alkyd-melamineresin comprising parts by weight of alkyd resin modified with non-dryingoil and/or non-drying oil fatty acid and having an oil length of 10 to30 and 20 to 60 parts by weight of melamine-formaldehyde resin,

3. bisphenol A-epichlorohydrine type epoxy resin having an epoxyequivalent of 800 to 4,000 100 parts by weight of this resin being usedwith 20 to 60 parts by weight of butyl-etherified phenolformaldehyderesin or with 20 to 60 parts by weight of butyl-etherifiedurea-formaldehyde resin, and

4. oil free polyester-melamine resin comprising 100 parts by weight ofoil free polyester having an acid value of 5 to 20 and hydroxylequivalent of 400 to 1,300 and 20 to 60 parts by weight ofmelamineformaldehyde resin modified with an aliphatic monoalcohol havingfrom 1 to 4 carbon atoms.

2. A precoated metal sheet for producing a metal working productaccording to claim 1, in which said polyolefin sheet is one speciesselected from the group consisting of polyethylene and polypropylene.

1. A PRECOATED METAL SHEET FOR PRODUCING A METAL WORKING PRODUCT WHICHCOMPRISES A BASE METAL SHEET, A COATING FILM OF A THERMOSETTING RESINWHICH IS FORMED ON THE BASE METAL SHEET AND CURED TO SEMI-HARDENED STATEHAVING A TACKINESS OF FROM 2.0 TO 40 G/CM WIDTH AT A TEMPERATURE OF 25*CAND AT A RELATIVE HUMIDITY OF 75% AND A POLYOLEFIN SHEET REMOVABLYADHERED TO THE ABOVE SEMI-HARDENED COTAING FILM; SAID BASE METAL SHEETBEING ONE SPECIES SELECTED FROM THE GROUP CONSISTING OF MILD SHEET,ALUMINUM SHEET, CHLOMIUM-PLATED STEEL SHEET AND ZINCPLATE STEEL SHEET;SAID THERMOSETTING RESIN BEING ONE SPECIES SELECTED FROM THE GROUPCONSISTING OF
 1. THERMOSETTING ACRYLIC RESIN CONTAINING HYDROXYL GROUPIN THE MOLECULE AND HAVING AN ACID VALUE OF 5 TO 20AND HYDROXYL VALUE OF10 TO 70, 100 PARTS BY WEIGHT OF THIS RESIN BEING USED WITH 20 TO 60PARTS BY WEIGHT OF METAMINE-FORMALDEHYDE RESIN AND/OR NOT MORE THAN 20PARTS BY WEIGHT OF BISPHENOL A - EPICHLOROHYDRINE TYPE EPOXY RESINGAVING AN EPOXY EQUIVALENT OF 300 TO 800,
 2. ALKYD-MELAMINE RESINCOMPRISING 100 PARTS BY WEIGHT OF ALKYD RESIN MODIFIED WITH NON-DRYINGOIL AND/OR NONDRYING OIL FATTY ACID AND HAVING AN OIL LENGTH OF 10 TO 30AND 20 TO 60 PARTS BY WEIGHT OF MELAMINE-FORMALDEHYDE RESIN, 2.alkyd-melamine resin comprising 100 parts by weight of alkyd resinmodified with non-drying oil and/or non-drying oil fatty acid and havingan oil length of 10 to 30 and 20 to 60 parts by weight ofmelamine-formaldehyde resin,
 2. A precoated metal sheet for producing ametal working product according to claim 1, in which said polyolefinsheet is one species selected from the group consisting of polyethyleneand polypropylene.
 3. bisphenol A - epichlorohydrine type epoxy resinhaving an epoxy equivalent of 800 to 4,000 100 parts by weight of thisresin being used with 20 to 60 parts by weight of butyl-etherifiedphenol-formaldehyde resin or with 20 to 60 parts by weight ofbutyl-etherified urea-formaldehyde resin, and
 3. BISPHENOL A -EPICHLOROHYDRINE TYPE EPOXY RESIN HAVING AN EPOXY EQUIVALENT OF 800 TO4,000 100 PARTS BY WEIGHT OF THIS RESIN BEING USED WITH 20 TO 60 PARTSBY WEIGHT OF BUTYL-ETHERIFIED PHENOL-FORMALDEHYDE RESIN OR WITH 20 TO 60PARTS BY WEIGHT OF BUTYL-ETHERIFIED UREA-FORMALDEHYDE RESIN RESIN, AND4. OIL FREE POLYESTER-MELAMINE RESIN COMPRISING 100 PARTS BY WEIGHT OFOIL FREE POLYESTER HAVING AN ACID VALUE OF 5 TO 20 AND HYDROXYLEQUIVALENT OF 400 TO 1,300 AND 20 TO 60 PARTS BY WEIGHT OFMELAMINE-FORMALDEHYDE RESIN MODIFIED WITH AN ALIPHATIC MONOALCOHOLHAVING FROM 1 TO 4 CARBON ATOMS.
 4. oil free polyester-melamine resincomprising 100 parts by weight of oil free polyester having an acidvalue of 5 to 20 and hydroxyl equivalent of 400 to 1,300 and 20 to 60parts by weight of melamine-formaldehyde resin modified with analiphatic monoalcohol having from 1 to 4 carbon atoms.